In some fields and/or circumstances, corrugated filter media, such as corrugated air filter media, is preferred over flat media. For example, it is generally preferable for air filters for gas turbines to include corrugated filter media. The corrugated media include corrugations having outer ridges, which will face the direction of the air flow in use, uniformly spaced apart from outer ridges of adjacent corrugations to define a pitch of the corrugated media. Each pair of adjacent corrugations defines a groove therebetween having an effective depth extending from the outer ridges to a floor of the groove. The effective depth of the grooves between adjacent corrugations is a parameter that determines whether corrugations will collapse under high static pressure from high air velocities and dust loadings. A known method of corrugating filter media is to pass the media through opposing heated rollers that have meshing teeth for forming the corrugations.
Corresponding reference characters indicate corresponding parts throughout the drawings.